1. Field of the Invention
This invention relates to new and improved sulfonated lignins useful as dye dispersants and to a process for improving the activity and heat stability properties of sulfonated lignins.
2. Description of the Related Art
Dyestuff compositions generally comprise a dye cake, i.e., of dyes and a dispersant and/or diluent. These dyestuff compositions are widely used to color both natural and synthetic fibers. In the dyestuff composition, the dispersant serves three basic functions: (1) it assists in reducing the dye particle to a fine size; (2) it maintains a dispersing medium; and (3) it is used as a diluent.
Dye dispersants are generally one of two major types: (1) sulfonated lignins from the wood pulping industry (via either the sulfite pulping process or the kraft pulping process) where lignocellulosic materials, such as wood, straw, corn stalks, bagasse, and the like, are processed to separate the cellulose or pulp from the lignin or (2) naphthalene sulfonates from the petroleum industry. The present invention relates to sulfonated lignin dye dispersants. Sulfite (or bisulfite) wood pulping process lignin is recovered from the spent pulping liquor, known as "black liquor," as lignosulfonates; whereas, kraft (or sulfate) wood pulping process lignin is recovered from the black liquor as the sodium salt of lignin (products marketed under the Indulin.RTM. mark by Westvaco Corporation). This recovered lignin is subjected to sulfonation or sulfomethylation for use as dye dispersants (products marketed under the Polyfon.RTM., Kraftsperse.RTM., and Reax.RTM. marks by Westvaco Corporation). As used herein, the term "sulfonated lignins" may be used generally to refer to lignosulfonates, sulfonated lignins, or sulfomethylated lignins as before described.
The advantages of employing sulfonated lignins as dispersants in dyestuff compositions are (1) availability and (2) unique physical properties, which include good compatibility to many dye systems and outstanding dispersant characteristics at ambient and elevated temperatures. There are, however, a number of disadvantages in employing lignins as dispersants, whether they are sulfite lignins or kraft sulfonated lignins. These negative factors include fiber staining (as lignin in dry powder form is brown in color) and heat stability (as the dyeing process is conducted at elevated temperatures) of the lignins employed. These adverse properties are troublesome to dyers and many attempts have been made to overcome these disadvantages.
A number of technological developments have resulted in new methods and processes to modify sulfonated lignins to reduce the negative aspects of employing such materials as dye dispersants without simultaneously causing any major adverse effects upon those properties which render sulfonated lignins desirable as dyestuff dispersants. U.S. Pat. No. 4,001,202 describes a process for preparing a sulfonated lignin with improved fiber staining properties useful as a dye dispersant by reacting lignin with an epihalohydrin. Also, U.S. Pat. No. 4,338,091 teaches reacting a modified lignin with sodium sulfite and an aldehyde; the lignin having been modified by a pretreatment with sodium dithionate.
Additional examples of reacting or modifying lignins to make them more suitable as dye dispersants include U.S. Pat. Nos. 4,184,845, 4,131,564, 3,156,520, 3,094,515, 3,726,850, 2,680,113, and 3,769,272. The art cited is meant to show the state of the art and is not intended to be all inclusive of lignin modifications.
Although the methods for treating and preparing sulfonated lignins described above offer some advantage during dyeing, none have produced a product possessing the improvements obtained by the improved products made according to the claimed process.
During the dyeing process, only the dye exhausts itself onto the fiber where it becomes an intimate part of the fiber. The lignin and other dyeing adjuvants, which are left in the exhaust liquor, need to be subsequently treated in primary and secondary waste treatment facilities. Although lignin is a natural material, lignosulfonates are considered relatively poorly biodegradable (albeit more biodegradable than synthetic dispersants from the petroleum industry), and they are often viewed as environmentally unfriendly as they often exceed the capacity of dye houses or municipality waste water treatment facilities.
One solution to this problem would be to increase the dye dispersant activity of lignin dispersants. (The term "activity" refers to the relative amount of dispersant required to function effectively. The less dispersant required to perform, the higher its activity; whereas the more dispersant required to perform, the lower is its activity.) Such enhanced activity would permit reduced dosages required for dyeing and thereby lessen the existing waste water treatment problems.
Therefore, it is the general object of this invention to provide sulfonated lignins of improved properties to enhance their usefulness as dye dispersants.
A particular object of this invention is to increase the activity of sulfonated lignin dispersants.
Another object of this invention is to provide a process for improving the heat stability of dye formulations including sulfonated lignins.
Other objects, features and advantages of this invention will be seen in the following detailed description of the invention.